In a battery system for an electrical vehicle described in JP-A-2002-84604, a cooling fan of a battery is provided to cool an electrical part and an electronic control unit. Specifically, the cooling fan is provided in a cool air passage for cooling the battery, and an electrical detector and the electronic control unit are arranged in the cool air passage to be cooled by air blown from the cooling fan. Here, the electrical detector is disposed for detecting a battery charge/discharge current, and the electronic control unit has a microcomputer for calculating a battery remaining capacity.
However, in this battery system, the equipments such as the battery, the electrical part and the electronic control unit are simply located in the cool air passage in block. In this case, a heat transmission area between this equipments and cool air is small. Therefore, cooling performance per volume is decreased. Furthermore, various equipments having different sizes are simply located in the cool air passage, the size of the battery system becomes larger.